The invention relates to an x-ray examination apparatus comprising a roentgenographic installation, an x-ray tube oriented toward the roentgenographic installation, a collimator or primary radiation diaphragm which is flange-mounted to the x-ray tube and adjustable by a motor via a follow-up motor controller, and a program control installation for effecting the automatic step-by-step shifting of the patient support relative to the roentgenographic installation and relative to the x-ray tube which is aligned with respect to the roentgenographic installation.
X-ray examination apparatus, which possess a program control installation for the automatic step-by-step displacement of the patient support relative to the roentgenographic installation and relative to the x-ray tube which is aligned to the roentgenographic installation, are preferably employed in the case of angiography of the extremities. In this examination apparatus, a contrast medium is injected into the vascular system to be examined; for example, into the leg artery, and the diffusion of the contrast medium is followed roentgenographically. For this purpose, photographs are prepared at brief, preselectable time intervals which permit statements regarding the nature and the chronological progression of the diffusion of the contrast medium in the vascular system. On account of the diffusion speed of the contrast medium, which is, in part, quite high in the larger vessels, sometimes not only are rapid photographic series with up to four images per second necessary, but also the photographic exposure field must be displaced, at predetermined time intervals of up to approximately two seconds between every two photographs, respectively, by the amount of the distance traveled in the meantime by the contrast medium.
Because of such rapid movement the procedure can no longer be precisely carried out manually; and, in the case of known x-ray examination apparatus, program control installations are employed which bring about the adjustment of the motor-displaceable patient support by a preadjustable distance between the individual photographic exposures. However, instead of this, the x-ray tube and the roentgenographic installation have also already been displaced while the patient support remains stationary.
It is a peculiar feature of this examination technique that, in particular in the case of examination of the extremities, the image quality becomes somewhat poorer from photographic exposure to photographic exposure. On account of the increasing tapering or reduction in size of the extremities, gradually a lateral halation of the examination area occurs. The x-radiation passing laterally by the extremity impinges on the image layer or film in a nonattenuated fashion. In the case of x-ray examination apparatus with automatic exposure timers, this leads to erroneous exposures of the examination area.